1. Field of the Invention
The present invention relates to a method and apparatus for producing plural-component filament or fiber yarns having individual constituent micro-denier sub-filaments or sub-fibers that are easily separated and, in particular, to a method and apparatus for extruding easily splittable plural-component fibers suitable for making nonwoven fabrics in a spunbond process or woven fabrics.
2. Description of the Related Art
Various attempts have been made to produce woven and nonwoven fabrics having improved characteristics, such as greater bulkiness and softness, superior flexibility and drape, and better barrier and filtration properties for use in products such as disposable absorbent articles, medical garments and filtration materials. It has been found that nonwoven fabrics having desirable qualities can be manufactured from splittable plural-component fibers. Such plural-component fibers typically include at least two different polymers arranged as microfilaments or segments across the transverse cross section of the fiber, which segments extend continuously along the length of the fiber. By separating these plural-component fibers into their constituent segments after extrusion, a fine denier fabric with desirable characteristics can be produced.
Such a finer denier fabric is difficult to produce without employing splittable plural-component fibers. Individual fibers having a transverse cross-sectional area comparable to a single segment of a plural-component fiber are difficult to manipulate and generally cannot withstand the drawing process applied to attenuate extruded fibers without breakage. The use of plural-component fibers permits formation of a finer denier fabric, because plural fiber segments are joined to each other during at least a portion of the drawing and attenuation process, thereby forming a thicker combined fiber that can more readily be drawn and attenuated. Once drawn, the plural-component fibers can then be split into very fine sub-fiber segments.
A known method of producing plural-component fibers includes side-by-side merging of a plurality of sub-streams of polymers into a combined conjugated stream in a counterbore of a spinneret. As shown in FIG. 1, sub-streams of two incompatible polymers (polymers A and B) are introduced into the counterbore 12 of a spinneret 10 and brought into contact with each other. As used herein in the context of polymers, the term xe2x80x9cincompatiblexe2x80x9d refers to different polymers that do not strongly bond or strongly adhere to each other, but that will cling or somewhat adhere to each other when adjacently extruded in a molten state from a spinneret and, when arranged side-by-side, can later be separated from each other with a limited degree of effort. The adjacent polymer sub-streams form a combined stream that flows through the orifice 13 of the spinneret, and the stream is then quenched to form a spun plural-component fiber.
The most common synthetic textile fibers used in fabrics are made from polymer materials such as nylon (e.g., nylon 66, nylon 6), polyester, polyolefin, and their copolymers. All of these polymers are melt spinnable. Some nonwoven fabrics made from carded or air-laid webs comprise rayon or acrylic fibers.
Many of the nonwoven fabrics made from melt-spinnable polymers are produced using a spunbond process. The term xe2x80x9cspunbondxe2x80x9d refers to a process of forming a nonwoven fabric or web from thin fibers or filaments produced by extruding molten polymers from orifices of a spinneret. More specifically, as shown in FIG. 2, a plurality of plural-component fibers is extruded through orifices of a spinneret to form a vertically oriented curtain of downwardly moving fibers. The fibers are quenched and then enter an air aspirator 14 positioned below the spinneret, which aspirator introduces a rapidly downward moving air stream produced by compressed air from one or more air aspirating jets. The air stream creates a drawing force on the fibers, causing them to be drawn between the spinneret and the air jet, thereby longitudinally stretching and transversely attenuating the fibers. The drawn fibers exit at the bottom of the jet or jets and are randomly laid on a forming surface 16, such as a moving conveyor belt, to form a continuous nonwoven web of fibers. The web is subsequently bonded using one of several known techniques to form the nonwoven fabric, e.g., by being pressed between a pair of hot calender rolls. Carded or air-laid webs can also be formed from these polymers.
In the case of woven fabrics, the extruded fibers are typically quenched and drawn prior to being wound on a bobbin. Thereafter, in a separate process, a conventional knitting or weaving technique is employed to form a woven fabric from the fibers.
A number of known techniques can be used to separate the individual segments of plural-component fibers prior or subsequent to formation of the fabric. Specifically, fiber segments can be separated by applying mechanical force to the fibers, such as high pressure water or air jets or air turbulence, beating, carding, calendering, or other mechanical working of the fibers. In the case of woven fabrics, the fabric can be brushed or sanded to abroad and separate fibers. Another process for separating segments of plural-component fibers involves applying a hot aqueous solution to the fibers to induce splitting or treating the fibers with chemicals. Specifically, the fibers may be transported through a hot water bath or sprayed with steam or a mixture of steam and air. Other techniques have also been proposed, such as developing a triboelectric charge in at least one of the components and/or applying an external electric field to the fibers. Alternatively, one of the components of the plural-component fibers can be dissolved by a solvent applied to the fiber, such that segments formed of the undissolved component remain.
The required treatment of the fibers in the fabric adds cost to the process and introduces the possibility of damage to the fabric. If chemical treatment is involved, loss of polymer results in certain cases, and the additional problem of recycling, disposal and handling of the chemicals exists. Moreover, limited or incomplete fiber splitting may result, depending on the particular polymers, the extrusion process, and the splitting technique applied. In particular, the extent of fiber splitting may be limited at higher spinning and web formation belt speeds, thereby constraining the rate at which the nonwoven fabric can be produced. These problems can be mitigated by forming plural-component fibers that are easily splittable.
It has been found by the present inventor that easier splitting of a bicomponent fiber comprising two adjacent segments formed of incompatible polymers can be achieved by keeping the polymer sub-streams separated from each other in the spinneret and merging the side-by-side sub-streams into a combined stream just below the face of spinneret from which the sub-streams are extruded via two separate orifices. As described in U.S. Pat. No. 5,093,061 (the ""061 patent), the disclosure of which is incorporated herein by reference in its entirety, by combining the sub-streams only after the sub-streams have been extruded, the adhesion between the sub-fibers is sufficiently light that the fiber splits substantially completely into the sub-fiber segments upon application of boiling water.
While the aforementioned patent discloses the technique of combining two streams below the spinneret to form an easily splittable bicomponent fiber, the process described therein has a number of limitations. Specifically, the process is limited to an arrangement wherein two sub-streams are aimed directly toward each other (i.e., the sub-streams are directed along axes that intersect, the axes being co-planar in a vertical plane), such that substantial surface areas of the sub-streams come into contact with each other at the point of sub-stream intersection to produce a side-by-side two-segment fiber.
The geometry (i.e., co-planar intersecting axes) of that system is not readily extendable to production of multi-component fibers. In particular, the technique disclosed in the ""061 patent cannot be used to generate plural-component fibers having an elongated or ribbon-shaped transverse cross-section with three or more sub-fibers or segments, since the polymer streams merge at a common point. Further, while the degree of sub-fiber adherence is reduced by joining the polymer sub-streams below the spinneret, the centerline intersection of the sub-streams causes the sub-fibers to contact and adhere to each other over a substantial portion of their surface areas, thereby forming a significant bond.
Moreover, the system disclosed in the ""061 patent involves winding the two-segment fiber onto a package immediately after quenching of the fiber without splitting the fiber. The unsplit fiber is subsequently woven or knitted, and split only when the resulting woven fabric is subjected to boiling water in a scouring and dying process. It is desirable that the sub-fibers of the two-segment fibers be sufficiently bonded to each other to avoid separation during the winding, handling and weaving processes that occur prior to the dying process. Thus, the ""061 patent does not suggest fiber splitting in the context of spunbond or nonwoven fabric formation, where splitting in line with fiber extrusion is desirable.
Acordingly, there remains a need for a system capable of producing easily splittable plural-component fiber useful for in-line fiber splitting in a simple, inexpensive and rapid spunbond process to form nonwoven fabrics having a fine denier and good fabric characteristics.
It is an object of the present invention to produce plural-component synthetic fibers whose constituent sub-fibers or segments are easily separated from each other, which fibers are useful for forming woven and nonwoven fabrics.
It is another object of the present invention to minimize the contact surface area between adjacent segments of a plural-component fiber to improve the separability of the segments.
It is another object of the present invention to produce plural-component fibers having a high aspect ratio, such as ribbon-shaped fibers, to improve process efficiency and fabric quality.
It is a further object of the present invention to achieve a high degree of separation between segments of plural-component fibers in an in-line spunbond process to produce a nonwoven fabric having a fine denier.
It is a still further object of the present invention to rapidly separate constituent fiber segments of plural-component fibers in an in-line spunbond process using a relatively simple, reliable and inexpensive mechanism.
It is another object of the present invention to produce a nonwoven fabric having superior properties, such as good coverage (i.e., no openings or gaps), bulkiness, softness, flexibility and drape, and good barrier properties.
It is yet another object of the present invention to form a fiber web that can more readily be bonded to form nonwoven fabric.
The aforesaid objects are achieved individually and in combination, and it is not intended that the present invention be construed as requiring two or more of the objects to be combined unless expressly required by the claims attached hereto.
According to the present invention, easily splittable plural-component synthetic fibers are formed by separately extruding individual molten polymer streams from orifices of a spinneret and joining the extruded polymer streams below the downstream face of the spinneret. The polymer streams are merged into a combined polymer stream by extruding the polymer streams in directions that cause surfaces of the streams to contact each other and adhere. The relative position of the orifices from which the polymer streams are extruded, the number of orifices, and the direction of extrusion of the individual streams determine the overall transverse cross-sectional shape of the resulting plural-component fiber. The centerlines of the extruded polymer streams are offset (i.e., non-intersecting) with each other, such that surfaces of adjacent streams contact each other in a somewhat tangential or glancing manner, thereby minimizing the surface area of each polymer stream that adheres to adjacent streams to facilitate subsequent easy separation of the fiber segments formed by the quenched streams.
According to an exemplary embodiment, a spinneret for producing easily splittable plural-component fibers includes two separate slot-shaped passages for respectively delivering two incompatible polymers (polymers A and B) to two sets of inclined capillaries. The two sets of capillaries converge toward each other in a downstream direction and direct molten polymer streams to two respective rows of orifices. The centerlines of polymer A capillaries lie along axes that, when extended beyond the spinneret, are offset and non-intersecting with axes along which the centerlines of the polymer B capillaries lie. Accordingly, in the direction of the rows of the orifices, the centers of the polymer A orifices are offset with respect to the centers of the polymer B orifices.
Polymers A and B are simultaneously extruded from their respective orifices at substantially the same speed in directions dictated by the angle and orientation of their respective capillaries. Consequently, the centerlines of the extruded polymer A streams are directed along axes that are non-intersecting with the axes along which the centerlines of the extruded polymer B streams are directed. The inclined angle of the capillaries and the arrangement of the orifices cause the extruded streams of polymers A and B to extend toward each other along offset centerline axes with the polymer A streams being directed between the polymer B streams in an interleaved fashion. The spacing between the orifices is set such that the polymer A and B streams contact each other in a generally tangential, glancing or grazing manner. More specifically, to ensure that the interleaved extruded streams of polymers A and B contact and adhere to each other to merge into a combined stream below the face of the spinneret, the distance b between the centerlines of adjacent same-polymer orifices is less than the sum of the polymer A orifice diameter and the polymer B orifice diameter.
The interleaved polymer streams contact each other to form a combined stream. The combined stream then proceeds substantially vertically downward and is subjected to a quenching process. By joining the polymer streams below the spinneret, adjacent segments of the resulting plural-component fiber are less strongly bonded to each other than they would otherwise be if joined within the spinneret and extruded from a single orifice. The offset arrangement of the orifices reduces the strength of the bond between adjacent fiber segments by limiting the surface area over which the segments are in contact with each other in the resulting plural-component fiber. The bond formed between adjacent segments of the plural-component fibers is sufficiently strong to withstand attenuation of the fibers without substantial separation, but sufficiently weak to allow separation with only a modest amount of separation processing.
Once quenched, the easily splittable plural-component fibers can be used to form a woven or non-woven fabric using any of a variety of fabric forming technologies. Likewise, the plural-component fibers can be separated using any one or a combination of known fiber-splitting techniques, including: mechanical working with high pressure water or air jets or air turbulence, beating, carding, calendering, and application of a hot aqueous solution, hot air and/or steam. In accordance with one embodiment of the present invention, in-line splitting of the plural-component fibers is accomplished using differential heat shrinkage in a spunbond process for forming nonwoven fabric.
The present invention is not limited to use of easily splittable plural-component fibers in nonwoven fabrics formed from spunbond process and encompasses processes for forming fabric from plural-component fibers that do not require bonding of the fibers (e.g., spun-laid or air carding processes). Further, the present invention can be applied in melt blown systems. The benefits of using easily splittable plural-component fibers are not limited to systems that form webs from fiber filaments (i.e., continuous fibers), and the present invention encompasses processes for forming woven and nonwoven fabrics from split or splittable staple fibers.
Further, formation of easily splittable plural-component fibers in accordance with the present invention can be performed in conjunction with other extrusion and fabric or material formation techniques. For example, both splittable and non-splittable fibers can be extruded from a single spinneret or plural spinnerets to create a web having a mixture of different types of fiber or fiber shapes. Further, a web formed from separated sub-fibers can be coupled to (e.g., bonded to) other types of webs or laminates in, for example, a multi-layered product.
The nonwoven fabric formed by the process of the present invention is useful in any product where properties such as softness, strength, filtration or fluid barrier properties, and high coverage at a low fabric weight are desirable or advantageous, including, but not limited to: disposable absorbent articles; medical barrier fabrics; filtration media; and clothing liners.